An RFID tag is disclosed adapted to be read by an interrogator including a reader antenna having a carrier frequency. The tag includes a first circuit including a first inductor and a first capacitor, wherein the first circuit is tuned to a frequency above the carrier frequency to compensate for detuning in the presence of a plurality of tags. The RFID tag includes a second circuit including a second inductor and a second capacitor wherein the first and second inductors are arranged to be coupled electromagnetically with a coupling factor less than unity and the second circuit is tuned to increase coupling between the first circuit and the reader antenna. A method of reading an RFID tag in the presence of a plurality of tags is also disclosed.
Legal claims defining the scope of protection, as filed with the USPTO.
1. An RFID tag adapted to be read by an interrogator including a reader antenna having a carrier frequency, said tag including: a first circuit including a first inductor and a first capacitor, wherein said first circuit is tuned to a frequency above said carrier frequency to compensate for detuning in the presence of a plurality of tags; a second circuit including a second inductor and a second capacitor; and wherein said first and second inductors are arranged to be coupled electromagnetically with a coupling factor less than unity and said second circuit is tuned to increase coupling between said first circuit and said reader antenna.
2. A tag according to claim 1 wherein said first circuit includes a chip.
3. A tag according to claim 2 wherein said chip includes said first capacitor.
4. A tag according to claim 1 wherein said coupling factor is substantially 0.7.
5. A tag according to claim 1 wherein said first inductor includes a first loop and said second inductor includes a second loop larger than said first loop.
6. A tag according to claim 5 wherein an edge of said first loop is aligned with an edge of said second loop.
7. A tag according to claim 5 wherein said first and second loops are concentric.
8. A tag according to claim 5 wherein said first and second loops are eccentric.
9. A tag according to claim 5 wherein said second capacitor includes a parasitic capacitor formed by capacitance between windings of said second loop.
10. A tag according to claim 1 wherein said first and second inductors are connected at a common tapping point.
11. A tag according to claim 1 wherein said first and second inductors are formed on a common substrate.
12. A tag according to claim 11 wherein said first and second inductors are formed on opposite sides of said common substrate.
13. A tag according to claim 11 wherein said first and second inductors are formed on the same side of said common substrate and are separated by an insulator.
14. A tag according to claim 1 wherein said first and second inductors are formed on separate substrates.
15. A tag according to claim 1 wherein said first and second inductors are wound in the same sense.
16. A tag according to claim 1 wherein said second circuit is tuned above the frequency of said first circuit.
17. A tag according to claim 16 wherein said second circuit is tuned between 80-160% above the frequency of said carrier.
18. A tag according to claim 1 wherein said first circuit is tuned between 10-50% above the frequency of said carrier.
19. A tag according claim 1 wherein said carrier is 13.56 MHz, said first circuit is tuned to between 15-20 MHz and said second circuit is tuned to between 25-35 MHz.
20. An optical data carrier including a tag according to claim 1 .
21. A method of reading an RFID tag in the presence of a plurality of tags by an interrogator including a reader antenna having a carrier frequency, said tag including a first circuit having a first inductor and a first capacitor, said method including the steps of: tuning said first circuit to a frequency above said carrier frequency to compensate for detuning in the presence of said tags; providing a second circuit having a second inductor and a second capacitor; electromagnetically coupling said first and second indicators with a coupling factor less than unity; and tuning said second circuit to increase coupling between said first circuit and said reader antenna.
22. A method according to claim 21 wherein said first circuit includes a chip.
23. A method according to claim 22 wherein said chip includes said first capacitor.
24. A method according to claim 21 wherein said coupling factor is substantially 0.7.
25. A method according to claim 21 wherein said first inductor includes a first loop and said second inductor includes a second loop larger than said first loop.
26. A method according to claim 25 wherein an edge of said first loop is aligned with an edge of said second loop.
27. A method according to claim 25 wherein said first and second loops are concentric.
28. A method according to claim 25 wherein said first and second loops are eccentric.
29. A method according to claim 25 wherein said second capacitor includes a parasitic capacitor formed by capacitance between windings of said second loop.
30. A method according to claim 21 wherein said first and second inductors are connected at a common tapping point.
31. A method according to claim 21 wherein said first and second inductors are formed on a common substrate.
32. A method according to claim 31 wherein said first and second inductors are formed on opposite sides of said common substrate.
33. A method according to claim 31 wherein said first and second inductors are formed on the same side of said common substrate and are separated by an insulator.
34. A method according to claim 21 wherein said first and second inductors are formed on separate substrates.
35. A method according to claim 21 wherein said first and second inductors are wound in the same sense.
36. A method according to claim 21 including tuning said second circuit above the frequency of said first circuit.
37. A method according to claim 36 wherein said second circuit is tuned between 80-160% above the frequency of said carrier.
38. A method according to claim 21 wherein said first circuit is tuned between 10-50% above the frequency of said carrier.
39. A method according to claim 21 wherein said carrier is 13.56 MHz, said first circuit is tuned to between 15-20 MHz and said second circuit is tuned to between 25-35 MHz.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
July 5, 2006
October 26, 2010
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